(1) Field of the Invention
This invention relates, in general, to apparatus for, and a method of, locating a metal stud covered over by, and located behind, a wall partition. Further, it relates to apparatus means and a method for locating the metal screws fastening wallboard or the like to metal studs so that such metal screws can be removed and the wallboard then removed essentially intact.
(2) Description of the Prior Art
With more recent building practices, particularly in commercial buildings, it has become somewhat common to provide metal, rather than wooden, studs or upright members in the outer or inner walls of the building. Nevertheless, the use of metal studs is not limited just to commercial buildings. Such members are rather commonly used in new, residential housing construction, and in rehabilitation of older building structures, e.g. in the conversion of schools and other structures to condominiums. In such cases as last mentioned, the old walls may, in fact, be left standing with metal studs and new wall structures merely attached thereto.
Regardless of the building structure involved, once the metal studs are installed, the next step is to install the wall surface members. Thus, to these metal studs are then fastened the panels or wallboard members, e.g. the commonly so-called "dry walls" or other wallboard forming the wall surface. The wallboard members are fastened to the metal studs by a plurality of vertically disposed spaced apart metal screws that are driven through the wallboard member into the upright metal studs which are spaced apart from one another in horizontal disposition along the length of the wall e.g., 16 inches, center stud to center stud. These metal screws are commonly driven into the wall by an electric drill. Nevertheless, the screw heads are generally recessed and taped or spackled over, after which they are hidden, in anticipation of painting or otherwise finishing the walls.
Once a wall is installed and finished, it is sometimes most difficult to locate the concealed metal studs. Nevertheless, it may become necessary from time-to-time for various tradespersons such as carpenters, electricians, cabinet installers, etc., to locate the studs or a particular stud, for various desired purposes. In some cases, it may be desirable to locate all the metal studs behind a particular wall surface and the metal screws holding it so that such a wallboard or the like can be removed intact and later re-installed. Such may be the case where an electrician or plumber may need determine the existence and location of wiring or piping behind a wall surface. Or, when demolishing a building, it may be desirable to remove a wall intact rather than destroying or mutilating it for safety or environmental reasons, e.g., where asbestos is of concern. Even a homeowner may from time-to-time desire to locate a particular stud in a wall to use such as a foundation for mounting objects, e.g. pictures, on the wallboard or other outer surface.
There are, in general, three methods of which I am aware used for locating wall studs. The most fundamental method used is to tap the wall with a hammer at spaced-apart locations horizontally while listening to the sound made, attempting thereby to sense a relatively solid sound which occurs when the hammer is tapped on the wallboard directly in front of a wall stud. This method is mostly trial and error and is sometimes quite frustrating. Although damage to the wall, if any, is generally slight, e.g., dents and scratches, and relatively easily repaired in most cases, a wall stud may be completely missed, depending on the interval or distance apart of the striking locations. Thus, it may be necessary for a person to go over the same wall distance several times, at different tapping intervals, before sensing what appears to be a solid sound. Also, some individual's ears are more attuned to sound differences than others. It is not unusual, moreover, to mistake a solid sound, and to drive a nail into the wallboard only to realize that the stud's location has been missed entirely, or only its edge has been located. When the stud is missed entirely, one must try to locate the stud once again by tapping at different intervals and a nail must again be driven into the wallboard at chosen locations to determine if the hidden stud has been located.
A second method is to drive a nail through the wallboard at spaced locations along a horizontal line until a wall stud is finally encountered. This method is somewhat akin to the first method and suffers from the same disadvantage. Seldom is one able to choose the correct spacing or interval, in the first place, to locate the stud immediately. Thus, the spacing between "nail holes" may need be adjusted, more or less, until a portion of the stud at least is located. Once a stud is located, its horizontal extents and its center line can then, however, be readily determined. And once the centerline of one stud is located, other studs can then be located provided such are properly located on standard centers. The main disadvantage with this method of locating studs is that it is not only somewhat frustrating but such method necessarily involves physical damage to the wall surface. Each of the nail holes driven into a wallboard not located over a stud must, in general, be plugged, and then painted over, or the wall otherwise finished depending upon the particular wall covering involved. Such a method is not at all desired where the wallboard is papered over. Moreover, although it may be possible to locate a stud by this method, and the method first described, neither is of any help in locating the nails or screws that may have been driven into the wallboard fastening such to the stud.
A third method of locating wall studs involves the use of so-called "stud finders". These devices typically comprise, in general, a magnet supported in a manner to pivot in the presence of magnetic material, e.g. a nail driven through wallboard into a wooden stud. Exemplary of such prior art devices are U.S. Pat. Nos. 2,933,679; 3,293,544; and 3,363,208. None of these patents, however, disclose a device such as is contemplated by my invention. Neither could any of the devices disclosed be used, it is believed, to locate a metal screw driven into a metal stud.
U.S. Pat. No. 2,933,679 discloses a stud finder which makes use of the concept that certain materials of ferrous metal, e.g., nails, screws, or the like are attracted to a magnetic. Thus, in general, the stud finder disclosed comprises an elongated magnet mounted for rotation within a housing. In use, the stud finder is simply grasped by the hand and is moved horizontally along the wall. As a hidden nail holding a wall board to a wooden stud is approached, the pivotally supported elongated magnet will pivot and will align itself with the embedded nail. Although such a device might be helpful in locating a metal stud itself, as desired in part herein, the device will not, however, be found useful to locate the metal screws driven into a metal stud. This is because the magnet in the stud finder device will, it is believed, be attracted to the stud itself, not being able to distinguish between the metal stud and the metal screws located therein. Thus, locating the metal screws in a metal stud for removing such and the wallboard intact would still be largely a hit-and-miss operation. Moreover, the device disclosed in that patent includes a magnet searching, in a sense, for metal attracted thereby whereas my invention does not operate in such a fashion. As disclosed more fully later, my invention instead provides metal particles that are attracted to the metal screws located in the metal stud, and as such the metal screws act like magnets.
In U.S. Pat. No. 3,293,544, there is disclosed a nail detector using metallic particles. The nail detector comprises, in general, a spool located within a case, having a transparent outer face. The spool has a centrally disposed opening which extends from adjacent the transparent outer face to the rear face of the case which is in contact with a wall. A coil is provided upon the outer circumference of the spool connected to a source of electric current. When the coil is electrically energized it creates a magnetic field and magnetically exercises a plurality of iron filings seen through the transparent face. The case is moved along the wall while the iron filings are energized. As a result, when the opening in the spool passes over a hidden nail head, the iron filings will have a tendency to collect over the nail head, due to the nail being magnetized. The inner wall of the spool surrounding the opening, however, and at the location of the nail head, will permit the iron filings only to gather around the opening. When a nail head is so located, a pencil is inserted into the opening whereby to make a mark on the wall, at the location of the nail head. Such a device as disclosed in the patent, however, could not be used, it is believed, to locate the metal screws previously driven into a metal stud. It could not distinguish the metal screw from the metal stud.
U.S. Pat. No. 3,363,208 discloses a stud finding device wherein an elongated multiple magnetic sensor provides discernible deflection towards a nail head by one and generally two of a set of vertically mounted magnets pivotally mounted within the sensor. Thus, a plurality of elongated magnets are mounted one above the other, along the length of a U-shaped body member, open at one face. Each magnet is mounted at its top edge for pivotal motion toward the open face, placed against a wall, when a nail is encountered, as the elongated stud finding device is moved along a wall in a vertically upright manner. As the stud finder passes a stud, ordinarily at least two nails will cause a magnet to pivot inwardly toward the nails. This action can be readily detected by feel or observed where the back edge of the body member is of a transparent material. Such a stud finding device is of no use, however, in locating the individual metal screws fastening the wallboard to the metal studs, and which screws are hidden from view behind spackling compound, tape and paint.